The present invention relates to improvements in steam heated dryers, particularly to improvements in paper or cardboard machine dryers. More particularly, the invention relates to improvements in rotary siphons which are used in such dryers to evacuate condensate which accumulates therein as a result of exchange of heat between a rotary cylindrical shell and steam which is admitted into the interior of the rotating shell, normally through a conduit whose axis coincides with the axis of rotation of the shell.
The condensate gathering and evacuating siphons which are used in the shells of paper or cardboard machine dryers comprise one or more hollow housings which are adjacent to but slightly spaced apart from the internal surface of the rotating shell so as to define with the internal surface a relatively narrow gap through which condensate can penetrate from the interior of the shell into the interior of the housing. The condensate which accumulates in the interior of the housing is evacuated by way of a conduit which extends axially and from the interior of the rotating shell. It is further known to introduce pressurized steam into the interior of the housing at a location which is spaced apart radially inwardly from the internal surface of the shell so that the admitted steam flows into the aforementioned condensate evacuating conduit and causes the housing to suck condensate from the internal chamber of the shell, through the gap and into the intake end of the conduit.
In accordance with a prior proposal, the housing of the siphon has a regular conical surface which is adjacent to the gap between the housing and the internal surface of the shell, and a concavely curved section which is located radially inwardly of the regular conical surface and merges gradually into the conduit for evacuation of collected condensate. A port is provided in the housing radially inwardly of the junction between the concavely curved portion and the conduit to admit steam which flows from the inrternal chamber of the shell and propels condensate from the gap toward and into the conduit. The direction of inflow of steam is substantially at right angles to the axis of the housing. In normal operation, the ratio fo condensate to admitted steam in the interior of the housing is betwen 75 to 85 and 25 to 15 percent. The admixture of steam to condensate in the housing of the siphon results in the establishment of a pressure differential between the steam in the interior of the shell and condensate in the interior of the evacuating conduit so that the condensate in the housing flows radially inwardly against the opposition of centrifugal force and toward the axis of rotation of the shell to be evacuated by way of that portion of the conduit whose axis coincides with the axis of the shell. If the shell contains a rather substantial quantity of condensate, the gap between the radially outermost portion of the housing and the internal surface of the shell is flooded so that steam which is admitted into the internal chamber of the shell cannot penetrate into and mix with the condensate in the housing. Consequently, the condensate cannot flow against the action of centrifugal force because the pressure differential between the internal chamber of the shell and the interior of the housing is too small. At such time, the port in the wall of the housing acts as an injector and is supposed to entrain droplets of condensate in a direction toward and into the interior of the evacuating conduit. When the flooding of the gap is terminated, the inflowing steam is again free to mix with the condensate which enters the housing by way of the gap so that the pressure differential between the interior and the exterior of the housing increases and the mixture of steam and condensate can flow radially inwardly from the internal surface of the shell toward the axis of rotation to be withdrawn by way of the aforementioned axially extending portion of the evacuating conduit.
The prior art of which applicant is aware at this time includes German Offenlegungsschrift No. 2 413 271, German Offenlegungsschrift No. 32 37 994, and U.S. Pat. No. 4,384,412.